This invention relates to an apparatus and a method for reducing in size a medical device such as a stent, stent-graft, graft, or vena cava filter. The apparatus may be used in particular for fastening a medical device onto a catheter.
Medical devices such as stents, stent-grafts, grafts, or vena cava filters and catheters for their delivery are utilized in a number of medical procedures and situations, and as such their structure and function are well known.
A stent, for example, is a generally cylindrical prosthesis introduced via a catheter into a lumen of a body vessel in a configuration having a generally reduced diameter and then expanded to the diameter of the vessel. In its expanded configuration, the stent supports and reinforces the vessel walls while maintaining the vessel in an open, unobstructed condition.
Stents are typically inflation expandable or self-expanding. Self expanding stents which are constrained by a sheath or other restraining means, must be provided in a reduced diameter.
An example of a stent described in PCT Application No. 960 3092 A1, published Feb. 8, 1996.
In advancing a stent through a body vessel to the deployment site, the stent must be able to securely maintain its axial position on the delivery catheter, without translocating proximally or distally, and especially without becoming separated from the catheter. Stents that are not properly secured or retained to the catheter may slip and either be lost or be deployed in the wrong location. The stent must be crimped in such a way as to minimize or prevent altogether distortion of the stent and to thereby prevent abrasion and/or reduce trauma of the vessel walls.
In the past, this crimping or size reduction has been done by hand often resulting in the application of undesired uneven forces to the stent. Such a stent must either be discarded or re-crimped. Stents which have been crimped or otherwise reduced in size multiple times can suffer from fatigue and may be scored or otherwise marked which can cause thrombosis. A poorly crimped stent can also damage the underlying balloon.
Recently, stent crimping devices have been disclosed in U.S. Pat. No. 5,546,646 to Williams et al, U.S. Pat. No. 5,183,085 to Timmermans et al., U.S. Pat. No. 5,626,604 to Coffone, Jr., U.S. Pat. No. 5,725,519, U.S. Pat No. 5,810,873 to Morales, WO 97/20593 and WO 98/19633.
A cam actuated stent crimper, shown in FIG. 1, employs a plurality of arc-shaped or curved slots with semi-circular ends, disposed such that each slot or cam engages a cam follower bearing 22. The arc-shaped or curved surfaces of the slots are inclined to be non-concentric relative to the axis of rotation 26, and therefore rotation of the cam plate 28 transmits equal radial displacements to the cam follower bearings 22, to simultaneously actuate a like number of linear bearings 24, which have their corresponding linear tracks or rails mounted on a fixed plate. As shown in FIG. 1 the cam plate rotary drive 29 comprises a pneumatic cylinder mounted on a pivot or trunnion, arranged with the cylinder rod connected rotatably to a short arm fixed rigidly to the cam plate. Accordingly, linear motion produced by the pneumatic cylinder translates into controllable arcs of motion of the circular cam plate, which has a projecting V-shaped profile on its outer edge in rolling engagement with three equally spaced rollers with mating inverse V-shaped profiles to provide precise rotatable support to the cam plate. Depending on the direction of rotation, the linear slides which each carry a radially disposed crimping blade, are either moved inwards to apply a crimping force to the stent, or outwards to release the stent. Also when crimping, depending on the degree of rotation of the cam plate, a specific radial crimping displacement may be obtained to match the diametral reduction required for any particular stent.
All U.S. patents and applications and all other published documents mentioned anywhere in this application are incorporated herein by reference in their entirety.